The purpose of this study is to develop, test, and validate measures of stage of change for medication adherence among those with human immunodeficiency virus type 1 (HIV). These measures will address adherence with antiretroviral medications for HIV and medications for prophylaxis of opportunistic infections, and will be theoretically based upon the transtheoretical or stages of change model. This theory has been successfully applied to the development of similar measures for many other health related behaviors. The measures to be developed here include; stage of change for medication adherence, processes of change, decisional balance for medication adherence, and temptations for nonadherence. These will be developed in a sample of approximately 150 HIV positive patients using standard psychometric techniques. Revised short form questionnaires will then be administered to a second sample of 150 HIV positive patients. These data will be used to confirm the expected structure of measures through the use of structural equation modeling. These data will also provide the means to compare intravenous drug users (IDU) and non-IDU on measures of readiness for medication adherence, decisional balance for medication adherence, use of stage appropriate processes of change, and temptations to discontinue medications. After completion of the short form questionnaire, a sub-sample of fifty patients will receive medications dispensed in containers with Mediation Event Monitoring Systems (MEMS) for electronic monitoring of actual number of doses taken. This objective measure of compliance will be used to validate self-report of stage of change for adherence with medication. This research will provide a foundation for future development of highly individualized interventions tailored to stage of change for the adoption of adherent medication taking behavior.